(a) Field of the Invention
This invention generally relates to field of devices for securing plastic components together, and more particularly, but not by way of limitation, to a system and method for connecting elements of plastic fence together.
(b) Discussion of the Prior Art
The advancement and development of modern plastic materials has allowed the substitution of an increasingly large number of materials with plastic materials. By substituting the material of manufacture to plastic one take advantage of the precision and efficiency of plastic molding processes.
As manufacturers seek more applications for plastics, the importance of understanding the properties of plastic materials becomes increasingly important since a straightforward substitution of plastic material for the traditional material is likely to result in an inefficient device which is likely to fail easily.
In recent years it has been recognized that plastic can be a durable, attractive substitute for wood in fencing applications. The ability of plastics, such as poly vinyl chloride or vinyl, to withstand the elements, as well as their ability to take on and hold popular colors, has prompted industry to recognize the need to provide quality plastic fence systems that make full use of the advantages of plastic materials. The marketplace, however, has repeatedly shown that it will not accept plastic items that do not look like items made from traditional materials. For example, with vinyl siding for houses, the challenge has been to produce durable plastic components that look like traditional wood board siding. Similarly, in the field of fencing, one of the key problems has been to provide plastic fence that looks like wood fence, but takes full advantage of the manufacturing and strength advantages of plastics.
In high volume manufacturing of plastic parts one generally tries to produce parts by means of extrusions or by means of molds. Extrusions use a die to continuously produce long parts with a desired constant cross-section. Molds are generally used produce individual pieces which contain features that do not allow manufacture of the part from extrusions. It is generally accepted that molds can be more expensive to manufacture than dies, and that the continuous fabrication of extrusions is more economical than the piecemeal fabrication accomplished by molding. However, molds can generally produce more precise parts than can be accomplished with extrusions. Thus it is advantageous to use extruded parts where tolerances are not critical since these can be significantly less expensive than molded parts. However, the mating of extruded parts to molded can pose problems due to the tolerances that must be taken into account when trying to match extruded parts.
In the field of fabrication of plastic fencing, for example, manufacturers have tried to keep the cost of fences down by using extruded sections where possible and molded parts where required. Thus, when providing plastic picket fencing it has been found that extruded sections have been used advantageously as plastic posts and plastic board or picket sections. However, these elements must include molded terminations and detailing that simulates wood picket fence, for example, in order to provide the same aesthetically pleasing effect as wood fencing. The combined use of extruded parts with molded parts has given rise to the need to devise an effective and economical system or method for joining molded and extruded parts, particularly parts for making fences.
One of the most common approaches at joining fence components has been to simply glue the components together. This approach, however, has some very serious drawbacks. Perhaps the most serious drawback being that the industrial glues and solvents used emit vapors that can pose serious health hazards to installers who are repeatedly exposed to the vapors while installing the fencing. Also, these glues do not dry instantly; therefore, the assembly process must be carefully coordinated in order to save time and achieve a quality product, without defects produced by shifting of the components while the glue cures. Moreover, the use of glues requires that the installer use care in not spilling or allowing the glue to run down the exposed areas of the fence. Still another disadvantage to glue is that it may not be practicable to correct a misplacement of parts once the adhesive cures.
In order to address the limitations of the use of adhesives, several attempts have been made at fabricating fence with the use of mating mechanical attachment means. Typically these attachments include integral spring tabs which bias pins or protrusions into recessions in a mating part. The field of plastic fabrication has typically taught the use of integral parts because of the economic advantages of incorporating several functions into a single part, which would reduce costs by requiring the manufacture of a single mold and obviate assembly steps.
Attempts at providing parts with mating mechanical attachment means have suffered from the tolerance requirements imposed by mating mechanical parts. For example, U.S. Pat. No. 5,421,556 to Dodge et al. teaches the use of a resilient cap with integral tab on an inside surface of the cap and which mates with a recession on an external surface of a post. An important limitation to this approach is the tolerances required for a quality, solid assembly. To join the assembly the integral tab must be positioned along the inner surface of the cap so that the tab reaches the recession when the cap is placed over the post. However, if too much distance is provided the cap will remain loose on the end of the post. If too little distance is allowed, the manufacturer runs the risk of providing caps that will not mate with the post, and thus result in wasted parts.
Other approaches, such as taught in U.S. Pat. No. 5,215,290 to Khalessi use external plastic components that reveal that the fence is plastic and not real wood, and thus are not aesthetically pleasing to many. Another approach taught in U.S. Pat. No. 4,553,741 to Creasy et al. uses slots in deformable plastic rails to interlock the rails in fabricating fence sections. This approach also suffers from the limitation that it easily detected as a plastic fence.
Other approaches, such as those taught in U.S. Pat. Nos. 4,477,058, 4,124,198, and 3,700,213 teach the use bulbous projections that are inserted into an orifice in the mating component. These approaches, however, require extensive use of molded parts, which do not take full advantage of the economical advantages of extruded parts.
Thus, there remains a need for a simple, secure system and method for joining sections of plastic fence so that the extrusions can be used where possible and molded parts used only where required. Moreover, there remains a need for an effective system and method for solidly joining components of fencing without the use of glues. Still further there remains a need for a strong system and method for joining plastic fence components that can be quickly installed with little need for special skills on the part of the assembly person.